A Brief Introduction to Add-Ons (2nd edition)

2: A Simple Add-On.

This Add-on consists just of a star with a single planet orbiting around it. It uses a Star Catalog and a Solar System Catalog.

For this and other Add-ons to work properly, you should download and install Celestia v1.3.0 (or a newer version) if you haven't already done so. Many addons require this newer version of Celestia in order to work. Nebula definitions, for example, can't work with version 1.2.5. See section 5 for details.

As the first step in this Add-on, create the directory \extras\addons\HIP500000\ (That's "HIP5" followed by 5 zeros.)

Your directory structure might look something like this:

[-] Celestia130
    --- data
    [-] extras
     |  [-] addons
     |      --- HIP500000
    --- models
    [+] textures

(The HIP500000 directory does not need any subdirectories. The surface texture this Add-on uses is one that comes with Celestia.)

Within the HIP500000 directory, create two Catalog files:
2.1: A STar Catalog (STC), which tells Celestia where to draw the star.
2.2: A Solar System Catalog (SSC), which tells Celestia where to draw planets around the star.

2.1: An STC file

Hipparcos satellite

Imaginary stars have to be given fake Hipparcos numbers in Celestia. Usually people use numbers between 300000 and 600000.

Here is a very simple STC file which defines the star named "HIP 500000".

Put this STC file into the directory \extras\addons\HIP500000\

This STC file contains the information Celestia needs to draw a star. However, Celestia ignores everything on a line after the #. Those are "comment lines".

If you type this in by hand, be sure to get the Capitals and spaces right. "{" and "}" are the letters "shift-[" and "shift-]" These squiggly-brackets are important: they tell Celestia where the definition of each object begins and ends. I usually use "Select-and-Paste" commands so I know everything got copied exactly right.

#######################
#hip500000.stc
#######################
# HIP 500000
500000 {		#Hipparcos number of star
	RA  98.0	#Right Ascension of star, measured in degrees
	Dec  5.04	#Declination of star
	Distance  5500	#Distance to star, measured in Light Years
	SpectralType "G0"	#may also include its Luminosity Class
	AppMag 15	#Apparent Magnitude of star as seen from Earth
} 
#######################

hip500000.stc

If you're using Celestia v1.3.0, its STC files can only include the Hipparcos index number. Names have to be added to the file starnames.dat.

If you're using Celestia v1.3.1pre3 or newer, its STC files can include both a star's Hipparcos index number and its name.

The star's name must follow the Hipparcos number, be enclosed in quotes, and come before the first "{". More than one name can be specified between the quotes if they're separated by colons (:).

For example, here's how you could define Intro as the name for the star HIP 500000:

#######################
#hip500000.stc
#######################
# HIP 500000
500000 "Intro" {	#Hipparcos number and name of star
	RA  98.0	#Right Ascension of star, measured in degrees
	Dec  5.04	#Declination of star
	Distance  5500	#Distance to star, measured in Light Years
	SpectralType "G0"	#may also include its Luminosity Class
	AppMag 15	#Apparent Magnitude of star as seen from Earth
} 
#######################

Now start Celestia and type the commands [return] HIP 500000[return]

HIP can be spelled hip -- capitals don't matter here.
One space between HIP and the number is needed to match the number declared in the .STC file.
[return] stands for the large "Carriage-Return" key at the right edge of the main part of your keyboard. Sometimes it's labelled "Enter".
When you type the first [return], Celestia will prompt with "Target name:". It wants you to type the name of the object to be "Selected". You can type just another [return] if you don't want to change the selection.

This star name (HIP 500000) should appear in the top left corner of Celestia's window. This means that the star is "Selected".

If this does not happen, there may be some mistakes in the STC file you made, or you might have put it in the wrong folder. Look at it very carefully. Capitals matter. Quotes (") matter. Don't add spaces in the middle of the command words.

Now type a "G" to GoTo that star. Celestia should turn and go flying to it. You should see a brightly glowing star just like our Sun, with sunspots but no planets.

Exit from Celestia.

2.2: An SSC file

Put this .SSC file into the directory \extras\addons\HIP500000\ where you already put hip500000.stc.

This .SSC file only includes the barest minimum of declarations that Celestia really needs for it to draw a planet. All of the other things that people put into .SSC files just make a planet look better or make it follow precisely the orbit that astronomers have measured.

The lines starting with a # are not needed. They're known as "comment lines." Everything on a line following a # is ignored by Celestia.

If you type this file in by hand, be sure to get the Capitals and spaces right. "{" and "}" are the letters "shift-[" and "shift-]" These squiggly-brackets also are important: they tell Celestia where the definition of each object begins and ends. I usually use "Select-and-Paste" commands so I know everything got copied exactly right.

#########################
# hip500000.ssc
#########################
"b" "HIP 500000" {
	Texture "jupiterlike.jpg"
	Radius 64000 
	EllipticalOrbit
	{	Period 5.8
		SemiMajorAxis 2.5
	}
}
#########################

hip500000.ssc

Now your directory structure should look something like this:

[-] Celestia130
    --- data
    [-] extras
     |  [-] addons
     |      --- HIP500000
     |           -- hip500000.ssc
     |           -- hip500000.stc
    --- models
    [+] textures

Start Celestia.
GoTo HIP 500000 as you did in step 2.1 above.

Open the menu "Navigation" "Solar System Browser" after you GoTo the star. It should list all of the planets around the star: just "b" in this case.

GoTo the planet. Play with the Render settings.

Here's a snapshot taken by Celestia of this solar system:
[HIP 500000 and planet b]
HIP 500000 and its planet "b"
and here's a Cel://URL to take you to this viewpoint:
HIP 500000 and its planet "b"